Detection of cadmium by a fiber-optic biosensor based on localized surface plasmon resonance

A novel transmission-based localized surface plasmon resonance (LSPR) fiber-optic probe has been developed to determine the heavy metal cadmium ion (Cd(II)) concentration. The LSPR sensor was constructed by immobilizing phytochelatins (PCs), (γGlc-Cys)8-Gly, onto gold nanoparticle-modified optical fiber (NMAuOF). The optimal immobilizing conditions of PCs on to the NMAuOF are 71.6 μg/ml PCs in pH 7.4 PBS for 2 h. The absorbability (change of light absorption) of the PC-functionalized NMAuOF sensor increases to 9% upon changing the Cd(II) level from 1 to 8 ppb with a sensitivity of 1.24 ppb−1 and a detection limit of 0.16 ppb. The sensor retained 85% of its original activity after nine cycles of deactivation and reactivations. In addition, the sensor retains its activity and gives reproducible results after storage in 5% d-(+)-trehalose dehydrate solution at 4 °C for 35 days. The dissociation constant (Kd) of the immobilized PCs with Cd(II) was about 6.77 × 10−8 M. In conclusion, the PCs-functionalized NMAuOF sensor can be used to determine the concentration of Cd(II) with high sensitivity.